The polar vortex is an area of cold low pressure that typically circulates around the Arctic during the winter, spreading tentacles of cold southward into Europe, Asia, and North America at times. Except this time, it’s not a small section of the vortex, but what one forecaster, Ryan Maue of WeatherBELL Analytics, called “more like the whole enchilada” [that's visiting the eastern U.S.]

The next 48 hours look almost as bleak, with the temperature line staying below -18°C until around midnight Wednesday. Strangely enough, it just keeps going up from there, hitting the freezing mark on Friday morning.

So: two days of the coldest air anyone has experienced in Chicago since the 66 hour stretch we had in February 1996.